A measuring transducer of vibration type, especially a Coriolis, mass flow meter, is preferably used to ascertain a mass flow independently of the properties of the flowing medium, such as density, viscosity and/or flow profile. A further advantage of Coriolis, mass flow meters lies in the fact that the mass flow of a medium flowing through the measuring transducer can be measured without influencing the actual mass flow by a sensor immersed in the mass flow.
From DE 690 19 453 T2, a Coriolis mass flow meter is known, which has a mass flow tube coiled to a helix, wherein the helix includes a first loop and a second loop. An oscillation exciter, which is embodied as an electromagnetic exciter, acts between a peak of the first loop and a peak of the second loop. On a side of the helical mass flow tube lying opposite the oscillation exciter is arranged a securement element, which connects a peripheral point of the first loop with a neighboring peripheral point of the second loop. Furthermore, arranged between the first loop and the second loop are two capacitive sensors, which are arranged lying opposite one another on the helical mass flow tube, and which record change of distance with respect to time between the first loop and the second loop and forward this to a difference amplifier of a microprocessor.
If the mass flow tube when flowed through by a medium is made to oscillate in such a way that the first loop and the second loop oscillate relative to one another, the mass flow tube is acted upon by a Coriolis force, which, in addition to the oscillation of the two loops relative to one another, excites a torsional oscillation of the first loop and the second loop. Depending on which direction the first loop and the second loop move with respect to one another, due to the Coriolis forces which act upon the mass flow tube, there results a phase shift between the torsional oscillation of the first loop and the torsional oscillation of the second loop, which is recorded by the two sensors and forwarded to the microprocessor for processing, in order to determine from this phase shift a mass flow. Typically, for ascertaining mass flow value by the microprocessor, the oscillation exciter is tuned to a resonance frequency of the mass flow tube, in order to excite oscillations in the first loop and the second loop with as little energy loss as possible.
A disadvantage of such an arrangement is that, in addition to the oscillation excited by the oscillation exciter and the torsional oscillation of the two loops resulting therefrom, other oscillation modes of a higher order are excited, which can lead to an instability of the mass flow tube and, respectively, of its oscillation and/or torsional oscillation, and, thereby, to corruption of the mass flow value.